Generally, in a regulating valve, a valve stem is coupled to a valve body (plug) by engaging the valve stem with the valve body via screwing (see JP-A-60-146966). However, if the engagement is performed only by screwing, vibrations of the valve body caused when the regulating valve performs flow rate control of fluid may loosen the screwing. Accordingly, a pin is used as one means for preventing (locking) the screwing from being loosened in a conventional regulating valve.
FIGS. 12 and 13 illustrate examples of the coupling structure between a valve stem and a valve body in conventional regulating valves. FIG. 12 illustrates the coupling structure of a valve stem and a valve body of a conventional typical globe valve and FIG. 13 illustrates, the coupling structure of a valve stem and a valve body of a globe valve in which a bellows has been welded to a conventional valve stem.
As illustrated in FIGS. 12 and 13, in conventional regulating valves, after a valve body 91 is engaged with a valve stem 92 by screwing, through-holes 91A and 92A are formed in the valve body 91 and the valve stem 92 in the screwed region, respectively, and a pin 94 (for example, a taper pin or a spring pin) is inserted into the through-holes 91A and 92A to prevent the screwing from being loosened between the valve body 91 and the valve stem 92.